1. Field of the Invention
This invention relates generally to plasma processing systems, and more particularly to plasma processing systems for maintaining a constant set-point temperature from wafer to wafer in plasma processing.
2. Description of the Related Art
High density plasma (HDP) processing systems are used to process semiconductor wafers or substrates for fabrication of integrated circuits. For example, high density plasma processes are commonly used in etching, oxidation, chemical vapor deposition (CVD), etc. The high density plasma processes are typically carried out by means of plasma processing systems and generally include a plasma processing chamber to provide a controlled setting.
FIG. 1 illustrates a schematic diagram of a conventional high density plasma processing system 100 for processing a wafer 106. The plasma processing system 100 includes a plasma processing chamber 102 and a pair of RF power generators 104A and 104B. The plasma processing chamber 102 includes an electrostatic chuck (ESC) 108 for holding and clamping the wafer 106 in place during plasma processing. The RF power generator 104A generates and provides RF power to an electrode 114 provided in the electrostatic chuck 108. An ESC power supply 122 is arranged to generate and provide a DC voltage to the electrode 114 to clamp the wafer 106 to the electrostatic chuck 108.
The plasma processing chamber 102 is configured to receive RF power from the RF power generator 104B and a source gas 116. When the RF power generators 104A and 104B are energized after the source gas 116 has been introduced into the plasma processing chamber 102, plasma 118 is generated from the source gas 116 over the wafer 106 and diffuses down to the wafer 106. In addition, the RF power provided to the electrode 114 produces ions 120 that bombard the wafer 106. In this manner, the plasma 120 and the ions 122 process the wafer 106 to produce desired plasma processing characteristics on the wafer 106.
During plasma processing, a heat transfer gas 110 such as helium is provided to the wafer 106 via a port 112 through the electrostatic chuck 112. The heat transfer gas 112 functions as a heat transfer medium between the wafer 106 and the electrostatic chuck 108 to keep the wafer 106 at a constant temperature during plasma processing. In general, this scheme keeps the wafer 106 at a reasonably constant temperature for plasma processing.
Conventional plasma processing chambers are typically used to process batches of wafers. For example, when a batch of wafers are processed, one after another, to produce integrated chips, it is desirable to keep the temperature of the wafers at a constant value. The uniformity in temperature helps to ensure fabrication of chips of uniform features across the batch of wafers.
Unfortunately, however, the conventional plasma processing system 100 often suffers from variation in wafer temperature during plasma processing from wafer to wafer due to several factors. For example, different wafers typically exhibit different resistivity, resulting in varying emissivity of RF radiation. Furthermore, the backside roughness of wafers is generally non-uniform for the wafers. On the other hand, various coatings on the front surfaces, i.e., surface being processed, of the wafers vary from wafer to wafer. In addition, different structures, devices, and materials on wafers and the aforementioned factors typically lead to varying wafer temperatures during plasma processing. As can be appreciated, the processing of wafers at such varying temperatures leads to different process performance.
In view of the foregoing, what is needed is a system and method for processing wafers at a constant temperature from wafer to wafer during plasma processing.
The present invention fills these needs by providing a system and method for providing a set-point temperature during plasma processing from substrate to substrate. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium. Several inventive embodiments of the present invention are described below.
In one aspect of the invention, the present invention provides a plasma processing system for providing a set-point temperature for substrates during plasma processing by controlling clamping force. The plasma processing system includes a plasma chamber, a controller, and an electrostatic power supply. The plasma chamber is arranged to receive an RF power and a source gas for producing plasma. The plasma chamber includes an electrostatic chuck for clamping a substrate in place during plasma processing. The electrostatic chuck includes an electrode and a sensor, which is arranged to monitor temperature of the substrate being processed. The controller is coupled to the sensor to receive the substrate temperature and is configured to generate a control signal for driving the substrate temperature to the set-point temperature. The electrostatic power supply is coupled between the controller and the electrode in the electrostatic chuck. The electrostatic power supply receives the control signal from the controller and generates a voltage adapted to clamp the substrate with a clamping force. In this configuration, the electrostatic power supply provides the voltage to the electrode to clamp the substrate such that the substrate temperature is driven to the set-point temperature.
In another aspect of the invention, the present invention provides a plasma processing system for providing a set-point temperature for substrates during plasma processing by controlling RF power. The plasma processing system includes a plasma chamber, an electrostatic power supply, a controller, and an RF power generator. The plasma chamber is arranged to receive a source gas for producing plasma and includes an electrostatic chuck for clamping a substrate in place during plasma processing. The electrostatic chuck includes an electrode and a sensor, which monitors the temperature of the substrate. The electrostatic power supply is coupled to the electrode to provide a voltage signal for generating a clamping force to clamp the substrate. The controller is coupled to the sensor to receive the substrate temperature and is configured to generate a control signal for driving the substrate temperature to the set-point temperature. The RF power generator is coupled between the controller and the plasma chamber. In this configuration, the RF power generator receives the control signal from the controller and generates an RF power adapted to control heat input to the substrate in response to the control signal. The RF power generator provides the RF power to the plasma chamber such that the substrate temperature is driven to the set-point temperature while generating the plasma from the source gas.
In yet another aspect of the invention, the present invention provides a method for providing a set-point temperature for substrates during plasma processing in a plasma processing system by controlling clamping force. The plasma processing system is arranged to receive an RF power and a source gas for producing plasma and includes an electrostatic chuck for clamping a substrate in place during plasma processing. The electrostatic chuck includes an electrode coupled to an electrostatic power supply to generate a clamping force for clamping the substrate. In this method, temperatures of a substrate being processed is monitored and received. In response to the monitored temperatures, a control signal is generated for driving the substrate temperature to the set-point temperature. The control signal is then provided to the electrostatic power supply to generate a clamping voltage. The clamping voltage is then provided to the electrode to generate a clamping force adapted to drive the substrate temperature to the set-point temperature.
In another aspect of the invention, a method for providing a set-point temperature for substrates during plasma processing in a plasma processing system by controlling an RF power. The plasma processing system is arranged to receive an RF power and a source gas for producing plasma and includes an electrostatic chuck for clamping a substrate in place during plasma processing. The electrostatic chuck includes an electrode coupled to an electrostatic power supply to generate a clamping force for clamping the substrate. The method includes: (a) monitoring temperatures of a substrate being processed; (b) receiving the substrate temperatures; (c) generating a control signal for driving the substrate temperature to the set-point temperature; and (d) providing the control signal to the RF power generator to generate an RF power adapted to control heat input to the substrate such that the substrate temperature is driven to the set-point temperature.
In yet another aspect of the invention, a plasma processing system for providing a set-point temperature for substrates during plasma processing is described. The plasma processing system includes a plasma chamber, a controller, and a pressure controller. The plasma chamber is arranged to receive an RF power and a source gas for producing plasma and includes an electrostatic chuck for clamping a substrate in place during plasma processing. The electrostatic chuck includes an electrode and a sensor, which is arranged to monitor temperature of the substrate. A heat transfer gas is provided under the substrate for controlling temperature of the substrate. The controller is coupled to the sensor to receive the substrate temperature and is configured to generate a control signal for driving the substrate temperature to the set-point temperature. In response to the control signal, the pressure controller is arranged to adjust the pressure of the heat transfer gas that is provided under the substrate such that the substrate temperature is driven to the set-point temperature.
In some embodiments of the present invention, the systems and methods may monitor either the rate of temperature change or emissivity change of substrates. Advantageously, the present invention minimizes temperature variation from substrate to substrate during plasma processing by providing a controlled clamping force and/or RF power input. Specifically, the present invention allows plasma processing of substrates at a specified set-point temperature from substrate to substrate by monitoring the rate of temperature or emissivity changes during plasma processing. In response to the monitored rates, a controlled clamping force is applied to the electrostatic chuck to control the heat transfer from the substrate to drive the substrate to the set-point temperature. Similarly, an RF power may be controlled to regulate heat input to the substrate to drive the substrate to the set-point temperature. By thus providing a set-point temperature for substrates, the present invention substantially improves process uniformity and yield of substrates and wafers. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.